The present invention relates to a leak free floating packing shaft seal which can be utilized for large propeller shafts, such as those used by submarines in a deep ocean environment.
Shaft packing was used on submarines until after World War II. After World War II the shaft packing was replaced with mechanical face seals because of the leakage problem of shaft packing at greater depths. The disadvantages of the mechanical face seals are that they are expensive and have to be replaced often due to wear and corrosion problems. Also, the mechanical face seals are heavy, costly, distort under pressure and require secondary O-ring seal support for the seal ring. The mechanical face seals also require very careful experienced mechanics to assemble the split configuration over the shaft and there is no assurance that the surface dimensions are acceptable after assembly.
The shaft packing type of seal has many advantages over the mechanical face seals except that prior art shaft packing seals have unacceptable leakage problems at great water depths attainable by modern submarines. Regardless of whether the seal is a shaft packing seal or a mechanical face seal, it must be capable of accomodating radial movements of the shaft due to vibration and eccentricity. It is important that the radial movements of the seal be substantially free of axial loading due to differential pressures between the high pressure environment on one side of the seal and the low pressure environment on the other side of the seal. One such floating packing seal is illustrated in U.S. Pat. No. 4,177,997 to Cartwright. In this patent the holder of the packing is pressure balanced on the upstream and downstream sides of the holder so that the holder is capable of radial movement without the detriment of axial forces thereon. Unfortunately the patented holder provides no way of sealing the holder within a supporting structure to prevent the high pressure outside environment from imposing itself on the internal spaces of the ship or boat utilizing such structure. Also the patent does not provide for preventing extrusion of the packing under high pressures. If the sealing and extrusion problems could be overcome the packing tpe of floating shaft seal would be preferable to the presently used mechanical face seals for submarines since the packing seal would be lower in cost, be lighter in weight, and would have wear elements which are easier to replace.